Products made from paper webs such as bath tissues, facial tissues, paper towels, industrial wipers, food service wipers, napkins, medical pads and other similar products are designed to include several important properties. For example, the product should have a relatively soft feel, should be strong, and, for most applications, should be highly absorbent. High bulk is also often preferred in such products. For example, three dimensional, high bulk paper products are often preferred over thinner, more two-dimensional products.
Several methods have been proposed in the past for producing a high bulk paper product which is both soft and strong. These methods still present difficulties to be overcome, however, due to the fact that the two desired characteristics tend to be mutually exclusive. For example, the cost of increasing product strength is often a decrease in product softness. The reverse is also true, processes which may increase softness, such as addition of debonding agents to the fiber slurry or creping, tend to decrease product strength. Similarly, processes which may increase web strength usually involve an increase in the number of interfiber bonds and are often accompanied with increase in web density. Such strengthening processes may not only decrease product softness but also decrease product bulk.
A creping method to make both a strong and soft towel is disclosed in U.S. Pat. No. 3,879,257, issued to Gentile, et al., entitled “Absorbent Unitary Laminate-Like Fibrous Webs and Method for Producing Them.” Gentile, et al. discloses a process of creping a base sheet, printing a bonding material on one side of the base sheet, creping the base sheet again, printing a bonding material on the other side of the base sheet, and then creping the base sheet a third time. In particular, the base sheet is printed while traveling through gravure nip rolls. During the process, referred to as the Double Recrepe (DRC) process, the gravure print process compresses the base sheet to less than 50% of its incoming caliper as it prints the bonding material onto the sheet. The DRC process provides a web possessing a good combination of strength and softness, but the process of having, successively, three pressings does not provide a particularly bulky sheet.
More recently, through-drying has become an alternate means of drying paper webs. Through-drying provides a relatively noncompressive method of removing water from the web by passing hot air through the web until it is dry. More specifically, a wet-laid web is transferred from a forming fabric to a coarse, highly permeable throughdrying fabric and retained on the throughdrying fabric until fairly dry. The resulting through-dried web is bulkier than a conventionally dried and creped sheet because the web is less compressed. Squeezing water from the wet web is eliminated, although the use of a pressure roll to subsequently transfer the web to a Yankee dryer for creping may still be used.
While there is a processing incentive to eliminate the Yankee dryer and make an uncreped throughdried product, uncreped throughdried sheets are typically stiff and rough to the touch, compared to their creped counterparts. This is partially due to the inherently high stiffness and strength of an uncreped sheet, but may also in part be due to the coarseness of the throughdrying fabric onto which the wet web is conformed and dried. Softening processes, such as calendering or creping, while increasing product softness, will also increase density of the through-dried sheet, and decrease desired product bulk.
Accordingly, there is a need for a paper product, or paper sheet, that is soft, absorbent and strong, and more particularly, which has higher bulk than those products made conventionally using an uncreped through-dried process or a double recreped process.